1. Field of the Invention
The present invention relates generally to ocean thermal gradient power plants and more particularly to such plants containing a minimum of moving parts.
2. Description of the Prior Art
Conventional power plants, both fuel burning and nuclear, utilize a cycle known as the Rankine cycle in which water in evaporated at high pressure, passed through a steam turbine and condensed at a low pressure. In the late 19th century, the French physicist, D'Arsonval suggested a similar cycle using the warm surface water in the tropics as a heat source and the cold deep water as the sink but using a selected working fluid (refrigerant) instead of water, to obtain more favorable characteristics in machinery, notably a smaller turbine than would be used for low pressure steam, if it were produced. The Rankine cycle is a "closed" cycle, in which the same refrigerant or working fluid is recycled time after time. This requires large heat transfer surfaces to evaporate and condense the refrigerant. Such a plant suffers an initial disadvantage in poor efficiency because of small temperature differences (typically on the order of 22.degree.C or less), according to well recognized principles of thermodynamics, and the further deficiency of an upper limit in a "perfect" machine as described by S. Carnot. The potential for increased efficiency has moved the power industry to higher and higher boiler pressures and temperatures, and lower and better condensing temperatures to produce increasingly lower cost electricity. Modern steam plants are indeed efficient, and only because of drastically increasing fossil fuel costs has electricity become more expensive in the United States.
Unlike other power plants (except hydroelectric), the ocean thermal gradient power plant does not use fuel, but in its present closed cycle concepts requires a very expensive plant which until recently has been considered not to be cost effective. Many of these costs arise from the very large boilers and condensers necessary to achieve net power production and the very large anchors, moors, and structures necessary to contain the large machinery. In addition, large numbers of tubes in the boiler and condenser will foul with marine growth, a problem in conventional condensers using seawater as a coolant, and much worse in ocean thermal gradient closed cycle plants, as the surfaces will not be significantly warmer than the water, as they are in fossil fueled condensers.
A French scientist and engineer, George Claude, recognized the heat transfer problems, as he was somewhat of an expert for his time in the kind of evaporation and cooling of importance in the closed cycle plant, being a wealthy inventor who successfully liquified air. He chose to take a more direct route than suggested by D'Arsonval and in the 1920's built a plant on land in northern Cuba; he later did the same thing in a ship off South America. Rather than use of working fluid in a closed cycle, he chose to evaporate the warm, readily available surface water, pass it through a low pressure steam turbine and condense it with direct contact with cold water pumped from the deeps. The operation was not an overwhelming success as it failed to produce a system capable of displacing fossil fuel burning plants. Had Claude's overall operations been successful, extremely large turbines would have been required for producing the large blocks of power of interest to a late 20th century power-hungry civilization. They are simply beyond the present state of the art, although no one has shown them to be impossible designs.
While Claude's experiments were thermodynamic successes, they were ocean engineering disasters. To bring the cold, deep waters from the ocean's depths to the surface, Claude was forced to utilize very large pipes or syphons and these proved too fragile to withstand the ocean's forces.